Question about "pig rails"

Hubby is in the middle of building our whelping pen. It will be 3 1/2 feet wide, 8 3/4 feet long and 2 feet high. The actual Whelping area is 3 1/2 feet by 5 feet. Because we are putting a divider in. As the pups get older the divider can be removed to make a bigger area.

Anyway here is my question. How high up should the pig rails be? I have looked at several sites that show whelping boxes and describe them but not one of them has given a height as to the pig rails. We are a couple of days off from adding them so it is not a rush to need the info. I would just like to know before we need to add them.

Thanks in advance.
Nicole & Sheena (moms to be)

I haven´t seen that either but you should do it at a height where mom usually leans on so she leans on that and not on puppies.......... so perhaps measure what Sheenas height is while laying down and do that about middle ribs or so.......

too high might make her squish under it...... too low and the puppies can´t be there.........

That is what I was figuring too. The problem is figuring out how high is high enough for the pups to get under but low enough so Sheena can't. Uggg. lol I will get it figured. Thanks for the tips.
Nicole & Sheena (moms to be)